KR100293198B1 - Method for restricting oxidation and corrosion of iron pellet - Google Patents

Abstract

PURPOSE: A method for restricting oxidation and corrosion of iron pellet(direct reduced iron) by immersing in octadecylamine(C18H39N) or oleic acid(C18H3O2) is provided. CONSTITUTION: The method comprises immersing iron pellets in an oleic acid solution at 50-130°C for more than 1 minute; drying the iron pellet in inert atmosphere at temperatures of lower than 50°C.

Description

[Name of invention]

Inhibition of oxidation and corrosion of iron pellet

Detailed description of the invention

[Purpose of invention]

[Technical field to which the invention belongs and the prior art in that field]

The present invention relates to a method for inhibiting oxidation and corrosion of iron pellets, the main raw material of steel mills, and more specifically, iron pellets may be octadecylamine (Octadecyl-amine: C ₁₈ H ₃₉ N) or oleic acid (Oleic acid: C ₁₈ H). ₃₄ O ₂ ) relates to a method of inhibiting reoxidation of iron pellets and improving corrosion resistance by immersion in solution.

Iron pellets currently used in steel mills use direct reduced iron, which is produced by reducing iron ore to coal or gas below the melting temperature of iron.

Recently, advanced steel mills are adopting melt-reducing steel production methods such as mini mill (electric furnace) and Korex as next-generation steel technologies, and are accelerating the introduction of facilities and technology development. Especially, the trend of new expansion of mini mill (electric furnace) plant for thin slab manufacturing As a result, supply-demand of iron scrap, a raw material, is intensifying, and the use of iron pellets (directly-reduced iron), which can be an alternative source of iron, is increasing due to rising prices.

Since iron pellets are prepared by chemically reducing iron ore pellets, they exhibit a porous structure with many pores, and thus have a very large specific surface area per unit weight. Iron pellets (directly reduced iron) having such particle characteristics are very dangerous because they are chemically very reactive and are easy to reattribute when stored or shipped by ship.

In other words, the reoxidation of iron pellets occurs in a dry state and reacts with oxygen in the air to form oxides and generate heat as shown in Equations (1) and (2).

3Fe + 2O ₂ → Fe ₃ O ₄ + Heat (1)

2Fe + 3 / 2O ₂ → Fe ₃ O ₄ + Heat (2)

If the above reaction continues, it will ignite due to the characteristics of the iron pellets poor heat transfer properties. In the presence of moisture and oxygen, the iron pellets undergo corrosion reactions such as equations (3) and (4) to form hydroxides and generate heat, as shown in equation (3). In this case, hydrogen gas is generated by the reaction as shown in Formula (5).

In addition, when deposited in seawater, hydrogen gas is generated by a reaction as shown in Equation (6), so the risk of ignition increases due to contact with air.

4Fe + 4H ₂ O + 2O ₂ → 4Fe (OH) ₂ + Heat (3)

4Fe (OH) ₂ + 2H ₂ O + O ₂ → 4Fe (OH) ₂ + Heat (4)

3Fe (OH) ₂ + Heat → Fe ₃ O ₄ + 2H ₂ O + H ₂ (5)

3Fe + 4H ₂ O + Heat → Fe ₃ O ₄ + 4H ₂ (6)

Due to the instability of the iron pellets or corrosion reactions, there is a risk of fire during storage, handling, and transport, as well as the metallization rate decreases, the recovery rate of metals, productivity, cooling capacity, etc. during the operation of the steel mill are reduced. There is a problem that the consumption of the electrode, quicklime, refractory increases.

In order to solve the problems caused by the oxidation and corrosion of the iron pellets, a method of performing or proposed the natural aging (midrex) and air contact method (air aging) to form an oxide layer by titration method on the surface of the iron pellets passivation), CHEMAIRE process for coating water glass on iron pellet surface (Midrex Corporation patent), and method for coating wax on iron pellet surface (US Pat. No. 4,692,353) and the pressure of iron pellets above 650 ° C to reduce specific surface area. There is a hot forming method to be produced.

Natural aging and air contact, which form a very thin magnetite oxide layer on the surface of iron pellets, are poorly used to sell to neighboring steelworks due to poor corrosion resistance to water or seawater.

The CHEMAIRE process, developed by Midrex, is a method of forming a water glass film on the surface of iron pellets, which has good corrosion resistance to water but poor corrosion resistance to seawater, and is mainly used when sold to global demand.

Among the above mentioned methods, the hot forming method is to reduce the inner surface of the iron surface, which has good corrosion resistance against water or seawater, and has a very low water content of 3-4%. do. However, since iron pellets are molded and manufactured by applying pressure at high temperatures, many additional facilities and costs are required.

[Technical problem to be achieved]

In order to solve the above problems, the present inventors have conducted research and experiments and proposed the present invention based on the results. An object of the present invention is to deposit iron pellets in octadecylamine or oleic acid solution and then dry the iron pellets. It is intended to provide a method for improving the resistance to corrosion and corrosion resistance.

[Configuration and Function of Invention]

The present invention comprises the steps of immersing iron pellets in octadecylamine or oleic acid solution at 50-130 ° C for at least 1 minute; And drying the deposited pellets in an inert gas atmosphere of 50 ° C. or less. It relates to a method for inhibiting oxidation and corrosion of iron pellets comprising a.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The present invention relates to a method of improving iron pellets' resistance to corrosion and corrosion resistance by depositing iron pellets in octadecylamine or oleic acid solution for a predetermined time and then drying them sufficiently to form a coating.

In the present invention, the iron pellets are manufactured by a direct reduction method, and the iron ore pellets are prepared by heat treatment at a temperature of 950 ° C. for 5 hours under a hydrogen gas atmosphere.

Iron pellets are immersed in octadecylamine or oleic acid solution to prevent oxidation and corrosion of the iron pellets. At this time, the temperature of the octadecylamine or oleic acid in which the iron pellets are deposited is preferably 50 ° C-130 ° C.

When the said deposition temperature is 50 degrees C or less, the octadecylamine whose melting temperature is 57 degreeC will solidify and it will be in the state which cannot cover an iron pellet surface site | part. In addition, when the deposition temperature is 130 ° C or higher, since the self-combustion temperature of the iron pellets is about 140 ° C, the iron pellets are gradually oxidized from the surface of the iron pellets, resulting in a lowering of the metallization rate.

Moreover, in this invention, it is preferable to coat | cover and coat iron pellets in the said solution for 1 minute or more. If the deposition time of the iron pellets is less than 1 minute, it may not be able to sufficiently infiltrate and diffuse evenly to the numerous pores in the pellets and uniformly coat them.

According to the method of the present invention, when octadecylamine is used as the organic solvent, an organic coating is formed on the surface of the iron pellet and the internal pores are coated. In addition, when oleic acid is used, since its own melting temperature is low, the solution is present in a solution state, and thus has only the effect of covering the internal pores in the deposition treatment according to the present invention, but the effect of inhibiting the resistance to corrosion and corrosion resistance is comparable to that of the octadecylamine. not.

The coating and drying step as described above is preferably carried out in an inert gas atmosphere of 50 ° C. or lower, which is unstable for reoxidation if the iron pellet surface and interior are not yet completely coated after deposition. It is preferable to dry at a drying temperature of 50 degrees C or less in an inert gas atmosphere until.

When the drying temperature is 50 ° C. or higher, the coated octadecylamine or oleic acid is melted and separated from the iron pellets.

Iron pellets coated with the coating as described above is excellent in corrosion resistance to seawater as well as resistance to reoxidation, and thus is very suitable for improving the resistance and corrosion resistance of iron pellets prepared from iron ore pellets.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1

Effect of Deposition Solution and Deposition Time on Iron Pellets

Invention Example 1-4

Iron pellets were prepared by heat treating iron ore pellets at 950 ° C. for 5 hours under a hydrogen gas atmosphere. Iron pellets were immersed in each of the octadecylamine solution and the oleic acid solution heated to 80 ° C., and then taken out after 1 and 30 minutes, respectively, and maintained for about 5 minutes in a mesh container smaller than the average radius of the pellets. The solution that was absorbed excessively inside was removed and dried sufficiently under a nitrogen gas atmosphere of 50 ° C or lower.

Resistance to corrosion and corrosion resistance of coated iron pellets was immersed in a 3% NaCl aqueous solution similar to that of seawater for 10 minutes, and then investigated by the change of metallization rate (metal Fe / total Fe%) with elapsed time. Table 1 shows.

The metallization rate is calculated by using a wet analyzer to measure the metal Fe content and the total Fe content, respectively, by wet chemical analysis.

Comparative Example 1-2

Except that the deposition time was set to 10 seconds and was carried out in the same manner as in Inventive Example 1-4 and the metallization rate was measured and the results are shown in Table 1 below.

[Comparative Example 3-8]

Using stearic acid and lauric acid as the deposition solution, respectively, it was deposited for 10 seconds, 1 minute, and 30 minutes, and then taken out and treated. Table 1 shows.

[Prior Example 1]

[Immersion method]

The wax was heated and melted at 110 ° C., and iron pellets were immersed and held for 1 minute, taken out, and held for about 5 minutes in a mesh container smaller than the average radius of the pellets.

Thereafter, the sample was sufficiently dried in a nitrogen gas atmosphere of 50 ° C. or less, and then used as a test sample. Resistance to corrosion and corrosion resistance of coated iron pellets was immersed in 3% NaCl aqueous solution similar to seawater for 10 minutes, and then the change of metallization rate (metal Fe / total Fe%) with elapsed time was investigated in Table 1 below. Indicated.

[Conventional Example 2]

[CHEMAIRE LAW]

Iron pellets were immersed for 1 minute in a 3% SiO ₂ aqueous solution prepared by adding 34.2 g of water to 3 g of 38% water glass, and then taken out and held for about 5 minutes in a mesh container smaller than the average radius of the pellets. Thereafter, the mixture was sufficiently dried in a nitrogen gas atmosphere of 50 ° C. or lower, and used as a test sample.

The resistance to corrosion and corrosion resistance of the coated iron pellets was immersed in a 3% NaCl aqueous solution similar to seawater for 1 minute, and the change in metallization rate with elapsed time was investigated in Table 1 below.

As can be seen in Table 1, in the case of the sample treated with organic solvent octadecylamine or oleic acid according to the present invention for more than 1 minute, the metallization rate was improved by at least 87-88%. When the water glass was used as a solvent by the CHEMAIRE process developed by Midrex and the sample treated with wax in US Pat. No. 4,692,353, it was demonstrated that the longer the aging time, the better the corrosion resistance.

However, in Comparative Examples 1-3 having 10 seconds of immersion time, the metallization rate decreased according to the aging time, and in Examples 1 and 3, in which the immersion time was 1 minute, the metallization rate was significantly different according to the aging time. There was no. Therefore, when octadecylamine or oleic acid solution is used as the organic solvent, the deposition treatment time is preferably maintained at 1 minute or more.

On the other hand, in the case of the comparative example using stearic acid or lauric acid as the immersion solution, it can be seen that the corrosion rate decreases considerably since the metallization rate decreases rapidly as the aging time increases when the reaction conditions are the same.

Example 2

Oxidation and Corrosion Resistance of Iron Pellets with Different Deposit Temperatures

Invention Example 5-10

Iron pellets were immersed in octadecylamine solution and oleic acid solution at 55 ° C., 110 ° C. and 130 ° C. for 1 minute, respectively, and then taken out. The solution was removed.

Thereafter, the mixture was sufficiently dried in a nitrogen gas atmosphere of 50 ° C. or less, and then used as a test sample. The resistance to corrosion and corrosion resistance of the coated pellets was immersed in a 3% NaCl aqueous solution similar to that of seawater for 10 minutes, and then the change in metallization rate with elapsed time was shown in Table 2 below.

Comparative Example 12-15

Except for changing the temperature of the octadecylamine solution and oleic acid solution to 150 ℃, 170 ℃ was carried out in the same manner as in Example 5-7 and the metallization rate was measured and the results are shown in Table 2 below.

As shown in Table 2, when the temperature is about 130 ° C. or lower, the deposition solution maintained the metallization rate as high as 87% according to the aging time, but when the temperature was 150 ° C. or higher, the metallization rate decreased.

This means that the higher the temperature, the faster the diffusion rate of the solution and the shorter the time to penetrate into the pores inside the pellet. However, when iron pellets are deposited at high temperatures, the iron pellets are deposited from the surface of the iron pellets. Self-oxidation occurs gradually, so the metallization rate is rather lowered. Therefore, the temperature of the organic solvent solution is preferably maintained at 130 ℃ or less.

In addition, it can be seen that the oxidation degree of Fe ²⁺ decreases to a considerable level according to the metallization rate of about 87-88%.

[Effects of the Invention]

As described above, by treating the iron pellets by immersion in octadecylamine or oleic acid solution, the resistance and corrosion resistance to the reoxidation of the iron pellets can be improved, and thus, the stability of the iron source can be secured, as well as high stability. Productivity also increases as the metallization rate is maintained.

Claims (1)

Immersing the iron pellet in octadecylamine or oleic acid solution at 50-130 ° C. for at least 1 minute; And drying the deposited pellets in an inert gas atmosphere of 50 ° C. or less. Oxidation and corrosion inhibition method of iron pellets comprising a.